1. Field of the Invention
The present invention is generally directed to the handling of the wastewater product of a hydrocarbon synthesis reactor. More particularly, this process is directed to recycling the wastewater product of a hydrocarbon synthesis reactor located downstream of a gasifier back to the feed of the gasifier.
2. Background
The process and advantages of gasifying hydrocarbonaceous material into synthesis gas are generally known in the industry. In high temperature gasification processes, synthesis gas is commonly produced from solid combustible organic fuels, such as coal, residual petroleum, wood, tar sand, shale oil, and municipal, agriculture or industrial waste. Prior to the gasification step, these solid combustible organic fuels are commonly pulverized and mixed with water to form slurry. The solid combustible organic fuels, in slurry form, are then reacted with a reactive oxygen-containing gas, such as air or oxygen, in a gasification reactor to obtain the synthesis gas.
In the reaction zone of a gasification reactor, the solid combustible organic fuel is contacted with a free-oxygen containing gas, optionally in the presence of a temperature moderator such as stearn. In the reaction zone, the contents will commonly reach temperatures in the range of about 1,700xc2x0 F. (930xc2x0 C.) to about 3,000xc2x0 F. (1650xc2x0 C.), and more typically in the range of about 2,000xc2x0 F. (1100xc2x0 C.) to about 2,800xc2x0 F. (1540xc2x0 C.). Pressure will typically be in the range of about 1 atmosphere (100 KPa) to about 250 atmospheres (25,000 KPa), and more typically in the range of about 15 atmospheres (1500 Kpa) to about 150 atmospheres (1500 KPa).
In a typical gasification process, the synthesis gas will substantially comprise hydrogen, carbon monoxide, and lessor quantities of impurities, such as water, carbon dioxide, hydrogen sulfide, carbonyl sulfide, ammonia, and nitrogen. The synthesis gas is commonly treated to remove or significantly reduce the quantity of impurities before being utilized in a downstream process.
Perhaps the best known of such processes is the Fischer-Tropsch process which involves the catalytic hydrogenation of carbon monoxide to produce a variety of products ranging in size and functionality from methane to higher molecular weight compounds. The main product stream of a Fischer-Tropsch reaction or other hydrocarbon synthesis process will in general contain hydrocarbons, alcohols, other oxygenated hydrocarbons, and a wastewater product, or condensate. This condensate will typically comprise water and hydrocarbons, alcohols, other oxygenates as their solubility limits allow; water being the predominate component. The desired hydrocarbon product generally can be separated from the remaining liquid phase or condensate by means known in the art. The separation is usually not totally complete, though, and often the condensate will have present in it some of the lower molecular weight hydrocarbons and oxygenates in the liquid phase. This contaminated condensate is of little or no commercial value. The oxygenates are known to cause corrosion while the hydrocarbons may cause foaming. Thus, the condensate is normally passed to an expensive water treatment facility where it undergoes typical water treatment steps, such as alcohol stripping, anaerobic digestion and biological oxidation, in order to remove the contaminants from the clean water. This water treatment process involves high capital and operating costs, but in light of existing environmental regulations, the treatment is necessary and thus cannot be avoided.
The present invention is generally directed to handling the wastewater, or condensate, from a hydrocarbon synthesis reactor. More particularly, the present invention describes sending the wastewater to a gasifier and subsequently reacting it with organic fuel, steam and oxygen at high temperatures and pressures so as to convert the wastewater into synthesis gas.
Also encompassed within the present invention is a process wherein the wastewater of a hydrocarbon synthesis reactor located downstream of a gasifier is recycled back to the gasifier and subsequently reacted with organic fuel, steam and oxygen at high temperatures and pressures so as to convert the wastewater into synthesis gas.
A further aspect of this invention is treating the wastewater from a hydrocarbon synthesis reactor located downstream of a gasifier. The gasifier is located downstream of a solid combustible organic fuel slurry preparation stage. In this embodiment, the wastewater is recycled back to the slurry preparation stage, where the solid combustible organic materials are pulverized and mixed with process water and the wastewater to form slurry. The slurry is then fed to the gasifier where it is reacted with steam and oxygen at high temperatures and pressures so as to convert the wastewater, along with the solid combustible organic fuel, into synthesis gas. The oxygenates in the wastewater provide additional oxygen to the gasifier, and hydrocarbons in the wastewater increase the amount of organic fuel burned in the gasifier to produce syngas. This reduces the overall cost, while eliminating a significant amount of potential environmental liability.
The present invention nearly eliminates the need for fresh water and process water make-up to the slurry preparation step, and a wastewater discharge/treating facility when slurry preparation, gasification, and hydrocarbon synthesis processes are combined as set forth in the following description. These and other features of the present invention are more fully set forth in the following description of illustrative embodiments of the invention.